EIP-712 Signature Domain Replay

The application used the same EIP-712 domain separator on mainnet and on an L2 deployment. A signature intended for one chain was silently accepted on the other. User authorizations could be replayed across chains without their knowledge.

Industry

Web3

Scope

Application · Cryptography · Multi-chain

Timeline

R·Q1 → V·Q1 → R·Q1

Closed

Impact

Cross-chain replay

Any user signature valid on both mainnet and the L2 deployment

User-visible surface

Zero — attack is silent to the signer

Affected primitives

Order signing, permit approvals, delegated authorizations

Impact vectors

›Cross-chain signature reuse

Reproduction

Steps below reproduce the finding against a staging replica. Where the reproduction affected a shared component, coordination was arranged before execution.

01Collect a valid mainnet signature from a legitimate user action.
02Submit the same signed payload to the L2 deployment.
03Verify acceptance: transaction executes against the same signer identity.

Vulnerability

Reused domain separator (simplified)solidity

bytes32 constant DOMAIN_SEPARATOR = keccak256(
  abi.encode(
    keccak256("EIP712Domain(string name,string version,address verifyingContract)"),
    keccak256("Xyrix"),
    keccak256("1"),
    // NOTE: chainId omitted. Same separator on every chain.
    address(this)
  )
);

Mitigation

Client-side mitigation shipped and validated during the engagement. Reference patch below.

Chain-bound domain (post-fix)solidity

bytes32 immutable DOMAIN_SEPARATOR;
constructor() {
  DOMAIN_SEPARATOR = keccak256(
    abi.encode(
      keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
      keccak256("Xyrix"),
      keccak256("1"),
      block.chainid,
      address(this)
    )
  );
}
// outstanding signatures invalidated via nonce migration.

Retest & Verify

✓Cross-chain replay attempts rejected post-migration (signature does not verify).
✓Outstanding pre-migration signatures invalidated by nonce bump.
✓User-facing flows re-issued signatures transparently on next action.

Deliverables

▊Technical Report
▊Domain-separator migration plan
▊Outstanding-signature invalidation script
▊Retesting report

Sign-off

Handled by

Epulyx

Reviewed by

Nolan

Closed

Case closed after cross-chain replay path verified closed.

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